US7436582B2ExpiredUtilityPatentIndex 63
Fast dynamic gain control in a bidirectionally-pumped Raman fiber amplifier
Est. expiryNov 15, 2025(expired)· nominal 20-yr term from priority
H01S 3/094011H01S 3/06754H01S 3/094061H01S 3/302H01S 3/094046H04B 10/2916H01S 3/10015H01S 3/094096H01S 3/13013H04B 10/2942H01S 3/1001H01S 2301/04H04B 10/296
63
PatentIndex Score
2
Cited by
35
References
15
Claims
Abstract
The present invention provides methods and apparatuses for controlling a gain of a bidirectionally-pumped Raman fiber amplifier having both forward optical pumps and backward optical pumps. The overall gain is controlled by adjusting the forward optical pumps, while the power levels of the backward optical pumps are essentially fixed. Gain circuitry operates in an opened loop configuration and uses a predetermined function relating a power variation of at least one wavelength region with a pump power adjustment for at least one forward optical pump. Two approximate linear relationships between the input signal power variations and the required pump power adjustments are utilized in controlling the Raman fiber amplifier. Each approximate linear relationship includes at least one linear coefficient that relates a power variation for a specific wavelength region and a power adjustment of a specific Raman pump.
Claims
exact text as granted — not AI-modified1. A bidirectionally-pumped Raman amplifier that is responsive to an optical signal over an optical fiber facility of an optical fiber system, the optical signal having N optical signal channels, comprising:
at least one backward optical pump configured to inject backward optical power by a counter-propagating signal-pump optical interaction with the optical signal;
M forward optical pumps configured to inject forward optical power by a co-propagating signal-pump optical interaction with the optical signal;
a measurement unit configured to determine an input signal power variation for at least one wavelength region, the N optical signal channels being associated with K wavelength regions, K being at least one;
a control unit configured to:
determine a fixed backward pump power value for the at least one backward pump; and
determine a forward pump power adjustment for least one forward optical pump using a predetermined function that depends on the input signal power variation;
the at least one backward optical pump configured to adjust a backward pump power output in accordance with the fixed backward pump power value;
the at least one forward optical pump configured to adjust a forward pump power output in accordance with the forward pump power adjustment; and
the predetermined function comprising:
Δ
P
d
(
j
)
≈
∑
K
k
=
1
T
d
L
(
j
,
k
)
Δ
S
L
(
k
)
,
wherein k corresponds to a k th wavelength region, wherein j corresponds to a j th forward Raman pump, ΔS L (k) corresponds to the input signal power variation for the k th wavelength region as linearly scaled, ΔP d (j) corresponds to the forward pump power adjustment of the j th forward Raman pump as logarithmically scaled, and T dL (j,k) corresponds to a linear coefficient relating the forward pump power adjustment of the j th forward Raman pump and the input signal power variation for the k th wavelength region.
2. The bidirectionally-pumped Raman amplifier of claim 1 , the measurement unit comprising:
a coupler that obtains coupled optical signals from an optical fiber, the coupled optical signals having a portion of a total power of the optical signal channels;
a 1 by K band wavelength-division multiplexer (B-WDM) configured to partition the coupled optical signals into the at least one wavelength region; and
at least one photodetector configured to provide an indication of the input signal power variation.
3. The bidirectionally-pumped Raman amplifier of claim 1 , the control unit configured to utilize the predetermined function that is characterized by a linear relationship between the forward pump power adjustment and the input signal power variation of the at least one wavelength region.
4. The bidirectionally-pumped Raman amplifier of claim 1 , further comprising:
a calibration unit configured to:
configure the optical signal channels, a signal power being different from a reference point only in the k th wavelength region; and
determine the linear coefficient T dL (j,k) by calculating ΔP d (j)/ΔS L (k).
5. The bidirectionally-pumped Raman amplifier of claim 1 , further comprising:
a fiber delay line, between a coupling point of the measurement unit to the optical fiber facility and an injection point of the M forward Raman pumps, configured to compensate for an associated time delay associated with processing the optical signal by the control unit.
6. The bidirectionally-pumped Raman amplifier of claim 1 , the measurement unit determining the input signal power variation for one wavelength region (K=1) and the control unit utilizing the predetermined function comprising:
ΔP d (j)≈T d (j)ΔS L , wherein j corresponds to a j th forward Raman pump, ΔS L corresponds to the input signal power variation as linearly scaled, ΔP d (j) corresponds to the forward pump power adjustment of the j th forward Raman pump as logarithmically scaled, and T d (j) corresponds to a linear coefficient relating the forward pump power adjustment of the j th forward Raman pump.
7. The bidirectionally-pumped Raman amplifier of claim 1 , the control unit further configured to turn off all forward Raman pumps and further configured to adjust the fixed backward pump power for the at least one backward optical pump to obtain a gain for a specified channel load.
8. The method of claim 6 , further comprising:
a calibration unit configured to determine each linear coefficient T d (j) from at least one measurement from the optical fiber system.
9. The method of claim 6 , further comprising:
a calibration unit configured to determine each linear coefficient T d (j) from at least one known fiber parameter of the optical fiber system.
10. A bidirectionally-pumped Raman amplifier that is responsive to an optical signal over an optical fiber facility, the optical signal having N optical signal channels, comprising:
at least one backward Raman pump configured to inject backward optical power by a counter-propagating signal-pump optical interaction with the optical signal;
M forward Raman pumps configured to inject forward optical power by a co-propagating signal-pump optical interaction with the optical signal;
a measurement unit determining an input signal power variation for at least one wavelength region, the N optical signal channels being associated with K wavelength regions, K being at least one,
the measurement unit determining the input signal power variation for one wavelength region (K=1) and the control unit utilizing the predetermined function comprising:
ΔP d (j)≈T d (j)ΔS L , wherein j corresponds to a j th forward Raman pump, ΔS L corresponds to the input signal power variation as linearly scaled, ΔP d (j) corresponds to the forward pump power adjustment of the j th forward Raman pump as logarithmically scaled, and T d (j) corresponds to a linear coefficient relating the forward pump power adjustment of the j th forward Raman pump;
a control unit configured to:
determine a fixed backward pump power value for the at least one backward Raman pump; and
determine a forward pump power adjustment for each forward Raman pump using a predetermined function that depends on the input signal power variation;
the at least one backward optical pump configured to adjust a backward pump power output in accordance with the fixed backward pump power value;
each said forward Raman pump configured to adjust a forward pump power output in accordance with the forward pump power adjustment; and
a fiber delay line, between a coupling point of the measurement unit to the optical fiber facility and an injection point of the M forward Raman pumps, configured to compensate for an associated time delay associated with processing the optical signal by the control unit.
11. A bidirectionally-pumped Raman amplifier that is responsive to an optical signal having N optical signal channels, comprising:
a forward-pumped Raman fiber amplifier having at least one forward optical pump;
a backward-pumped Raman fiber amplifier having M backward optical pumps;
a measurement unit configured to determine an input signal power variation for at least one wavelength region, the N optical signal channels being associated with K wavelength regions, K being at least one;
a control unit configured to:
determine a fixed forward pump power for the at least one forward optical pump; and
determine a backward pump power adjustment for the at least one backward optical pump using a predetermined function that depends on the input signal power variation;
the at least one forward optical pump configured to adjust a forward pump power output in accordance with the fixed forward pump power value; and
the at least one backward optical pump configured to adjust a backward pump power output in accordance with the backward pump power adjustment; and
the predetermined function comprising:
P
d
(
j
,
t
)
≈
P
do
(
j
,
t
)
+
∑
K
k
=
1
T
d
L
(
j
,
k
)
[
S
L
(
k
,
t
-
T
)
-
S
L
0
(
k
)
]
,
wherein k corresponds to a k th wavelength region, t corresponds to a time instant, j corresponds to a j th backward Raman pump, P d (j,t) denotes a required power of the j th pump in a logarithmic scale, P d0 (j,t) and S L0 (k) denote a pump power and a signal power at a reference operating point, T dL (j,k) corresponds to a linear coefficient relating the backward pump power adjustment of the j th backward Raman pump and the input power signal variation for the k th wavelength region, S L (k,t−T) denotes a detected input signal power in the k th wavelength region as linearly scaled, and T denotes a time delay between a required pump power adjustment and a detected signal power variation.
12. The bidirectionally-pumped Raman amplifier of claim 11 , the control unit further configured to utilize the predetermined function corresponding to a linear relationship between the backward pump power adjustment and the input signal power variation of the at least one wavelength region.
13. The bidirectionally-pumped Raman amplifier of claim 11 , further comprising:
a calibration unit configured to:
configure optical signal channels, a signal power being different from a reference point only in the k th wavelength region; and
determine the linear coefficient T dL (j,k) by calculating (P d (j,t)−P d0 (j,t))/(S L (k,t−T)−S L0 (k)).
14. A bidirectionally-pumped Raman amplifier that is responsive to an optical signal over an optical fiber facility of an optical fiber system, the optical signal having N optical signal channels, comprising:
at least one backward optical pump configured to inject backward optical power by a counter-propagating signal-pump optical interaction with the optical signal;
M forward optical pumps configured to inject forward optical power by a co-propagating signal-pump optical interaction with the optical signal;
a measurement unit configured to determine an input signal power variation for at least one wavelength region, the N optical signal channels being associated with K wavelength regions, K being at least one;
the measurement unit determining the input signal power variation for one wavelength region (K=1) and the control unit utilizing the predetermined function comprising:
ΔP d (j)≈T d (j)ΔS L , wherein j corresponds to a j th forward Raman pump, ΔS L corresponds to the input signal power variation as linearly scaled, ΔP d (j) corresponds to the forward pump power adjustment of the j th forward Raman pump as logarithmically scaled, and T d (j) corresponds to a linear coefficient relating the forward pump power adjustment of the j th forward Raman pump;
a control unit configured to:
determine a fixed backward pump power value for the at least one backward pump; and
determine a forward pump power adjustment for least one forward optical pump using a predetermined function that depends on the input signal power variation;
the at least one backward optical pump configured to adjust a backward pump power output in accordance with the fixed backward pump power value;
the at least one forward optical pump configured to adjust a forward pump power output in accordance with the forward pump power adjustment.
15. A bidirectionally-pumped Raman amplifier that is responsive to an optical signal over an optical fiber facility of an optical fiber system, the optical signal having N optical signal channels, comprising:
at least one backward optical pump configured to inject backward optical power by a counter-propagating signal-pump optical interaction with the optical signal;
M forward optical pumps configured to inject forward optical power by a co-propagating signal-pump optical interaction with the optical signal;
a measurement unit configured to determine an input signal power variation for at least one wavelength region, the N optical signal channels being associated with K wavelength regions, K being at least one;
a control unit configured to:
determine a fixed backward pump power value for the at least one backward pump;
determine a forward pump power adjustment for least one forward optical pump using a predetermined function that depends on the input signal power variation;
the at least one backward optical pump configured to adjust a backward pump power output in accordance with the fixed backward pump power value;
the at least one forward optical pump configured to adjust a forward pump power output in accordance with the forward pump power adjustment; and
the control unit further configured to turn off all forward Raman pumps and further configured to adjust the fixed backward pump power for the at least one backward optical pump to obtain a gain for a specified channel load.Cited by (0)
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